The invention relates to a device for guiding and supporting the cable for actuating a front derailleur for bicycles.
Front derailleurs on bicycles serve the purpose of moving the drive chain between various chain wheels mounted on the pedal crank. These front derailleurs have a stationary part, a parallelogram mechanism, and a moveable part. The stationary part is connected to the bicycle frame, and a chain guide for interacting with the chain is mounted on the moveable part. In order to mount on the bicycle frame, the stationary part has a fastening clamp, of which the size also varies as a function of the diameter of the seat tube. To some extent the seat tube exhibits an oval cross section. In this case the stationary part is screwed to a soldered-on part that is attached to the seat tube; or a flexible clamp is used. The chain guide is adapted to the ratio of the number of teeth and/or the ratio of the diameters of the chain wheels. Racing bikes have typically two chain wheels, whereas mountain bikes have three chain wheels. The chain guide has suitably designed guide parts in the regions, in which contact with the chain occurs when changing gears. The seat tube on the bicycle has various angular positions in relation to the chain stay, a feature that has an additional impact on the design of the chain guide.
There exist a plethora of other embodiments of derailleurs as a function of whether the actuating cable is run either towards the bottom around the pedal bearing housing or towards the top following the seat tube. Finally, the derailleurs may be alternatively actuated from the retracted position into the extended position either by actuating the cable control device or by the force of the return spring.
The available design space, in which a derailleur can be housed, consists of the free space inside the chain wheels, outside the seat tube and above the pedal bearing housing as well as to a limited degree between the rear wheel tire and/or the mud guard and the seat tube. In this case a mountain bike has significantly more free space between the seat tube and the tire than a racing bike, where there is the tendency to push the rear wheel as far as possible in the direction of the pedal bearing, as a result of which the rear wheel tire comes very close to the seat tube.
EP 0 653 347 shows a derailleur that has a pronounced cable guide region on the inner tensioning arm. Hence, the tensioning arm is significantly enlarged and more expensive to manufacture. As a result of the one-piece connection between the originally rod shaped arm and the cable guide, there is no longer any disturbing resilience that could result in a loss in the actuating path of the cable control device.
EP 1 040 992 shows a removable cable guide adapter that, in addition to the advantages of a cable guide, also makes it possible to adapt the derailleur to various conditions with respect to actuating the cable. The drawback with this design is that all of the deformations at the adapter have a direct impact on the cable actuation system. In any case it has to be guaranteed that after the adapter is mounted on the actuating arm, said adapter is securely connected to this actuating arm; and it must be achieved without incurring a high cost in terms of construction.